Oscillator circuit



M y 935. P. o. FARNHAM 2,001,695

OSCILLATOR CIRCUIT Original Filed Jan. 8, 1932 Patented May 14, 1935 PATENT OFFICE OSCILLATOR CIRCUIT Paul 0. Earnhann. Boonton, N. J.., assignor, by mesne. assignments, to Radio Corporation of America, New York, Delaware Application January 8,

more particularly to tuned oscillator circuits which will automatically deliver higher voltages v as'the oscillator is tuned'to lower frequencies.

My copending application, Ser. No. 564,676,, filed September 23, 1931, describes and claims cs.- cillator circuits of this general type which, when incorporated in a superheterodyne receiver, tend to reduce-those: variations in audio output that. arise from. the-[decreased transmission of the lower carrier frequencies. The present invention relates to other circuit arrangements for effecting the desiredvariation, with frequency, of the oscillator output Voltage, Itis possible to' design an oscillator circuit and a. signal frequency circuit which exhibit a substantially constant frequency difference when tuned by similar sections of a. gang con; denser. I To obtain this effect, the inductance of the oscillator circuit is made substantially less than that of the signal frequency circuit, and a lagging condenser having a capacity several times that. of the tuning condenser is included .a's'a. series element of the oscillator circuit. As. the gang condenser is adjusted for. tuning, the presence of the series condenser in the timed circuit of the oscillator makes the value of the total capacity tuning the oscillator coil lag behind the value of vthe capacity tuning the radio ire-- quency circuits, and the. series condenser which thus makes it possible to employ a' single tuning control in superheter'odyne receivers will thereforebe designated, in the following specification andv claims, as the laggin condenser. Theoscillator circuits contemplated by the present invention are of this type and the desired frequency variation of the oscillator output voltage is obtained. bycouplinganother circuit of the os cillator acrossthe series lagging impedance of the resonant circuit.

An object of the invention is to provide an oscillator including aresonant circuit of the type including a series lagging condenser, and in which another circuit of said oscillator is coupled across the series lagging condenser. Another object of the invention isto provide an oscillator including a tuned grid circuit including a series lagging condenser, and in which the instantaneous alternating voltage on the plate is substantially equal to that developed across the lagging condenser.

These and other objects and advantages of the invention will be apparent from the following specification, when taken with the accompanying drawing, in which, j

N. Y., a corporation of 1932, SerialNo. 585,59

Renewed: March 16, 1934 v p g Claims, (c1. o. 2o)

' inventionrelates to oscillator circuits and Fig. 1, is a fragmentary circuit diagram of a superheterodyne receiver which includes an oscillator embodying the invention, and

Fig. 2 is a circuit diagram of another oscillator embodying the invention;

In the drawing, the reference numeral l identifies a vacuum tube vfor amplifying signal energy at carfierfrequency, the amplified energy being passed to the. detector tube 2 and there combined with local oscillationsgenerated by oscillator tube 3 to produce a beat or intermediate frequency With the exception of the oscillator circuits, this portion of the superheterodyne receiver 'may be of any appropriate design. In the typical arrangement shown the drawing, the input circuit of the carrier amplifier comprises'an inductance L and tuningcondenser C, the input circuit being connected or coupled in any appropriate manner to the antenna or collecting structure AG.

The plate circuit of amplifier I 'is coupled to the detector input cir'cuitL, C, which'may be, and preferably is, substantially identical with the amplifier input circuit, the adjustable capacities being usually provided by sections of a gang condenser, as is indicated by the broken line '4 which tinguished from the customary oscillator circuits,

the plate circuit is not coupled to the inductance Lo of the grid circuit but is coupled across the series lagging, condenser Cs. This coupling may comprise an inductance L2 connected across the condenser Cs and coupled to a winding L3 in the 1 plate circuit with substantially unity coupling. This close coupling may be-secured by employing twin windings, i. e., the inductances L2, L3 are wound turn for turn and'closely adjacent each other on the same form. The inductances L2, L3 constitute twin chokes having inductances of such relatively high value as to resonate with the series capacity Cs at a frequency substantially lower than the lowest frequency within the tuning range of the oscillator.

the cathode and the bias resistor l0 which is shunted by condenser II. The inductanceLi is preferably a twin winding, as above defined, ex-

tending along about one-tenth of the grid inductance Lo. 7

' It will be apparent that the substantially unity coupling between windings L2, L3 makes the instantaneous oscillatory voltageon the plate of? tube 3 substantially identical with that established at the junction of inductance Lo. and the lagging condenser Cs. When the resonant circuit is tuned to higher frequencies, the impedance r of the condenser Csdecreases and thereforethe voltage on the plate decreases. As a result, the current flow in the inductance Lo, and therefore in the output circuit, decreases at a morerapid rate than the rate of frequency increase and the current output falls off with increasing frequency. Other methods of coupling. the plate circuit across the lagging condenser Cs are possible and, in Fig. 2, a capacitive couplingv is illustrated. A coupling condenser 12 is connected between the plate and the junction of inductance Lo and the condenser C5, the condenser l2 having a low ime; pedance for oscillator frequencies. A choke .13 is included in the plate circuit connection to a positive potential source which is indicatedby the legend EB. The usual grid resistance R is shunted across the laggingcondenser Cs to complete a direct circuit for the application of thebias voltage to the grid. I

Typical values of circuit constants which .will give satisfactory operationinthe circuit of Fig. 1 are as follows: 7 Tube.3=Type 227 Condenser Cs=about 3.3 times the maximum value of C Inductance L=aboutf75% of theinductance L Resistance |0=5000 ohms r Condenser |l=0.1 microfarad Resistance 8:5000 ohms Condenser 9:1000 micromicrofarads EB=90 volts In the circuit shown in Fig. 2," the coupling condenser l2 may be about 0.1 microfarad, and the choke I3 isan inductance of such value as to resonate with condenser Cs at a frequency below the tuning range of the oscillator. 1

It will be understood that the magnitude of condenser CS may be varied to aline .the oscillator circuit to track with the carrier frequency circuits but, once alined, the. value of Cs remains fixed and the only adjustmentof the oscillator circuit in the reception of signals is that provided by the uum tube having plate and grid elements and a cathode; and a resonant circuit between cathode and grid comprising an inductance shuntedby'a series lagging condenser in series with a tuning condenser; the junction of said condensers having an oscillator-frequency connection to the cathode, and. the junction of the inductance and u, tuning condenser beingconnected to the grid; of

means coupling the plate circuit across said 56- .tuning range of said oscillator.

ries lagging. condenser, said means comprises a transformer having one winding in the plate circuit and a second winding shunted across said series lagging condenser.

2. The invention as set forth in claim 1, wherein the windings of said transformer resonate with said lagging condenser at a frequency substantially lower than the lowest frequency within the 3. The invention as set forth in claim 1, wherein the windings of said transformer are twin windings wound turn for turn on the same form and having an inductance resonating with said lagging condenser at a frequency below the tuning range of said oscillator.

4. In a variable frequency oscillator adapted for the generation of voltage which increases with decreasing frequency, the combination with atube having a cathode, a control electrode and a plate electrode, of impedance elements forming a circuit tunable over a band of frequencies and connected between said cathodeand control 7 electrode, said circuit including as a series element a composite impedance resonantto a fre-i quency lower than the lowest frequency of said band of frequencies, and means coupling said plate electrode to said composite impedance.

5. The invention as set forth-in claim 4, wherein said composite impedance comprises a. fixed inductance shunted by a relatively fixed capacity. 6. In a variable frequency oscillator adapted for the generation of voltage which increases with decreasing frequency, the combination with a tube having a cathode, a control electrodeand a plateelectrode, of impedance elements forming a'circuittunable overa band of frequencies and connected between said cathode and control electrode, said circuit including as a series element a fixed inductance shunted by a. relatively fixed condenser, said series element being resonant to a frequencybelow the lowest frequencyof said band of frequencies, and means coupling said plate electrode to said series element, said coupling means to the series elementbeing the sole coupling between said plate electrode and .the elements of said tunable circuit.

7. In a variable frequency oscillator adapted for the generation of voltage which. increases with decreasing frequency, the combination with a tube having a cathode, a control electrode and a plate electrode,'of impedance elements forming a circuit tunable over a band of frequencies and connected between said cathode and control electrode, said circuit including as a series element a fixed inductance shunted bya relatively fixed condenser, said series element being resonant to a frequency below the lowest frequency of 'said band of frequencies, means coupling said plate electrode to said series element, and voutputvoltage terminals coupled to a second inductance in said tunable circuit. 1

8. In a superheterodyne receiver of the single control type, the combination of a carrier wave circuit andan oscillator circuit adaptedto be tuned over approximately the same frequency bands, each-circuit including an inductance and a tuning condenser, the tuning condensers being difference between the resonant frequencies of said circuits as said resonantfrequencies' are varied by adjustment of said tuning condensers, an oscillator tube having a cathode cooperating with a grid electrode and a plate electrode, a connection for maintaining the cathode and the junction of said lagging condenser and its associated tuning condenser at the same oscillator frequency potential, circuit connections for establishing at one electrode the oscillator-frequency potential'of the junction of the inductance and tuning condenser of the oscillator circuit, coupling means for coupling the other electrode to the junction of the lagging condenser and the inductance of the oscillator circuit, and a first detector tube for combining carrier waves transmitted by saidcarrier wave circuit with the oscillatory voltage developed by said oscillate tube. 7 PAUL O. FARNHAM. 

